The present disclosure relates to time integrators integrating time axis information and ΔΣ time-to-digital converters performing ΔΣ modulation of the time axis information.
In recent years, with the development in mobile communication techniques, the performance of A/D converters used for communication systems has been rapidly improved. Out of them, ΔΣ A/D converters are particularly widely used for the communication systems, since they are less subject to output distortion and relatively easily provide higher SN ratios. See, for example, Jose M. de la Rosa, Sigma-Delta Modulators: Tutorial Overview, Design Guide, and State-of-the-Art Survey, IEEE TRANSACTIONS ON CIRCUITS AND SYSTEMS. I: REGULAR PAPERS, VOL. 58, NO. 1, JANUARY 2011, pp. 1-21.
ΔΣ A/D converters require integrators. In general, operational amplifiers in which a capacitive element is inserted in a negative feedback path is used as integrators. That is, an input signal is converted to a current to charge and discharge the capacitive element, thereby integrating the input signal.
In recent years, as miniaturization in LSIs progresses, the operating voltages of the LSIs have been reduced. Thus, the SN ratios of signals are becoming difficult to improve in signal processing in a voltage direction. There is a dire need to process signals using the analog quantity along the time axis, that is, time axis information. The time axis information defined here is obtained by performing phase modulation of edges of clock signals with an information signal. So far, however, no promising circuit has been suggested as a circuit integrating time axis signals. In providing a ΔΣ time-to-digital converter processing time axis information, the time axis information needs to be converted back to voltage signals for integration.
Therefore, there is a need for a time integrator integrating time axis information represented by a phase difference between two signals, and a ΔΣ time-to-digital converter performing ΔΣ modulation of the time axis information.